Hevea brasiliensis is a tree originating in the Amazonian region. The milky sap of this tree, known as the latex, comprises about 33% rubber, 65% water and 2% protein. The rubber, known as latex rubber or natural latex rubber or sometimes simply as "latex", is chemically known as 1,4-cis-polyisoprene. Latex rubber may be isolated from latex by a variety of processes and incorporated into many manufactured articles. The world production of latex rubber is on the order of 6 million tons per year, and one major use of latex rubber is in the manufacture of gloves, known as latex gloves. With modern society's anxiety about transmission of viral and bacterial infection via contact with contaminated body fluids, the use of latex gloves has become an increasingly prevalent standard operating procedure for many workers.
Since about 1979, there have appeared numerous reports of severe anaphylactic reactions to medical devices, e.g., gloves, manufactured from Hevea brasiliensis latex, and this has prompted much concern in the medical community. See, e.g., Sussman et al. "The Spectrum of IgE-mediated Responses to Latex" JAMA 265:2844-2847, 1991. Research has indicated that these allergic reactions are the result of sensitization to proteins present in latex rubber. It is generally the case that when rubber is isolated from the latex, proteins that are also found in the latex, known as latex proteins, are isolated with the rubber and become incorporated into articles made from latex rubber.
Initially, it was believed that only one or a very few of the latex proteins were the offending allergens. However, an increasing number of research studies demonstrate that many latex proteins can serve as allergens. See Beezhold et al., "Identification of a 46-kD latex protein allergen in health care workers", Clin. Exp. Immunol. 98:408-413 (1994). This may be due, in part, to the process used to isolate latex rubber from Hevea brasiliensis, which relies upon added ammonium hydroxide to stabilize the latex. The ammonium hydroxide is thought to denature the latex proteins from their native configuration to produce a mixture of polypeptides. The denatured peptides are readily absorbed into skin and apparently are highly immunogenic.
Several approaches have been examined by the latex device manufacturing industry to overcome the problem of latex protein sensitivity. One approach has been to subject the latex article, e.g., gloves, to multiple leaching or washing steps. As part of the washing, chlorination of the product has become common practice. While this approach can effectively reduce the protein levels in the end product, it also weakens the latex film and reduces the barrier properties of the product. The additional washing and chlorination steps increase production costs because of the expense of increased processing and higher failure rates.
Another approach which has been explored is the use of proteolytic enzymes to degrade the proteins in latex. However, this approach has the problem of introducing another protein (the enzyme) to the latex, which may itself be allergenic.
Recognition of the sensitivity problem has prompted suppliers of latex rubber to search for isolation/purification processes that are more effective at separating latex protein from latex rubber. A currently popular approach is to subject the latex to a double centrifugation regime. Latex suppliers report that this regime reduces protein levels by 50%, however that contention is questionable.
There is thus an increasingly recognized need in the art for latex rubber-containing devices, including latex gloves and condoms, which can serve as effective barriers to bacterial and viral transmission, and which do not cause unwanted allergic reactions.